Upon sending service request via website, the Nokia Mobile Care replied;Please disable the Dolby >do a soft reset> holding the power off button and the volume up button for 10 sec until you feel a vibration and see the android logo >enable the Dolby again.

Unfortunately this did not solve the problem, but when disabling Dolby the volume is back to normal level. So that is a good workaround for now.

Lol dolby atmos tuning is actually an expensive tech to pay for, they have to hire dolby technician to fine tune the audio according to the audio behavior of each phone with their sophisticated algorithm. They introduced it in nokia 6 because it was the first phone of nokia hmd comeback so they wanted to make it great. Later, they used their own ozo audio later on on other devices to save cost.